Effects of N-(2-ethylhexyl)-3-hydroxybutyramide hydrogen succinate on the metabolisms of monoamines in the rat brain.

N-(2-Ethylhexyl)-3-hydroxybutyramide hydrogen succinate (M-2H) has been reported to increase REM sleep. The effects of M-2H on the metabolisms of monoamines which have been implicated in the regulation of the sleep-wakefulness cycle were studied in rats. M-2H (500 mg/kg p.o.) increased the levels of 5-hydroxyindoleacetic acid (5-HIAA), homovanillic acid and 3-methoxy-4-hydroxyphenylethyleneglycol sulfate in various regions of the rat brain. However, no appreciable changes occurred in levels of serotonin (5-HT), norepinephrine, dopamine, or 3,4-dihydroxyphenylacetic acid. The effect of M-2H (500 mg/kg p.o.) on 5-HT metabolism was investigated with intraventricularly-injected [14C]-5-HT. Although [14C]-5-HT level was not significantly changed, [14C]-5-HIAA level was above control level in four brain regions such as the hypothalamus, hippocampus, midbrain and pons-medulla at 3 h after the administration of M-2H. M-2H retarded the efflux of intraventricularly-injected [14C]-5-HIAA in all brain regions except the cortex. These results suggest that M-2H preferentially impaired the transport system for acid metabolites of monoamines, resulting in increase of monoamine metabolite levels in the brain.